Low power ultra wideband transceivers

ABSTRACT

Low-power transmitter and/or receiver devices are provided by sacrificing time and/or frequency diversity in exchange for lower power consumption. When channel conditions indicate that time and/or frequency spreading are unnecessary for transmissions, a transmitter may enter into a power-conservation mode in which transmissions are performed using a time gating scheme or a time repetition scheme. In the time gating scheme, symbols are transmitting just once, rather than a plurality of times, but with increased transmission power. In the time repetition scheme, copies of the same symbol are transmitted a plurality of times on the same frequency on different symbol transmission periods, instead of being retransmitted on different frequencies on different symbol transmission periods. Consequently, the symbol can be generated once and stored for subsequent retransmission, thereby allowing some of the transmitter/receiver chain components can be operated at a lower duty cycle or processing speed to conserve power.

CROSS REFERENCE TO RELATED APPLICATION & PRIORITY CLAIM

This patent application is a continuation of U.S. patent applicationSer. No. 12/369,926, filed 12 Feb. 2009, issuing as U.S. Pat. No.8,102,929 on 24 Jan. 2012, which is hereby incorporated by referenceherein for all purposes and as if set forth below in its entirety.

TECHNICAL FIELD

Various features pertain to ultra wideband communications. At least oneaspect pertains to an ultra wideband transceiver having improvedlow-power consumption enabling efficient wireless communications.

BACKGROUND

Ultra-wideband (UWB) is a radio technology that can be used forhigh-bandwidth communications by using a large portion of the radiospectrum (e.g., bandwidth of 500 MHz or greater). UWB communicationstransmit in a way that does not interfere largely with other moretraditional “narrow band” and continuous carrier waves in the samefrequency band. Generally, the Federal Communications Commission (FCC)defines UWB as a system using a bandwidth that exceeds the lesser of 500megahertz (MHz), or 20% of the center frequency. The FCC uses −10 dBemission points to determine bandwidth, and to define the centerfrequency. UWB technology may be applicable to high and low data ratepersonal area networks (PANs). The advantage of the large bandwidth isthat the system should be able to deliver high date rates over shortdistances, while sharing the spectrum with other communications systems.For this reason, the FCC has authorized the unlicensed use of UWB in theband between 3.1 gigahertz (GHz) and 10.6 GHz. UWB can be generated as apulse type system, where each transmitted pulse occupies the entire UWBfrequency bandwidth. An aggregation of narrowband subcarriers are usedto generate at least 500 MHz of frequency bandwidth. For example, anorthogonal frequency division multiplexing (OFDM) system may be used.OFDM splits the digital information to be transmitted over a pluralityof parallel slower data rate streams. Each of the parallel data streamsis modulated onto a particular subcarrier, using a technique such aquadrature phase shift keying (QPSK) for example, and transmitted at arelatively low data rate. The subcarrier frequency is chosen to minimizecrosstalk between adjacent channels, which is referred to asorthogonality. The relatively long symbol duration helps minimize theeffects of multipath, which is the degradation caused by signalsarriving at different times.

The UWB European Computer Manufacturers Association (ECMA) 368 standardis an example of a wireless standard that seeks to implement UWB.

One challenge with the current UWB technology is that it may consume toomuch power to be efficiently implemented on mobile devices (e.g., mobilephones, personal communication devices, mobile computing devices, etc.)that have limited power sources. That is, current consumption of UWBtransceivers may not be suitable for mobile devices.

Consequently, improvements to UWB transceivers are desirable to achievelower power consumption. Preferably, such improvements to UWBtransceivers would substantially comply with, or are compatible with,existing UWB standards.

BRIEF SUMMARY OF SOME EMBODIMENTS

According to one feature, a transmitter device and/or method areprovided for achieving power conservation. In some examples, thetransmitter and/or method may be operated in an ultra wideband spectrumto transmit orthogonal frequency-division multiplexing (OFDM) symbols. Awireless channel characteristic is determined, ascertained, or obtainedbetween the transmitter device and a receiver device. Determining thewireless channel characteristic may include ascertaining a desiredsignal strength (between the transmitter and receiver) and at least oneof: a channel noise, a noise floor, or an interference level.

A first mode of symbol transmission may be selected in which at leastone of time spreading and frequency spreading is enabled at a particulartransmission rate if the wireless channel characteristic is above athreshold level. A symbol may be transmitted using at least one of timespreading and frequency spreading if the first mode of symboltransmission is selected.

A second mode of symbol transmission may be selected in which at leastone of time spreading and frequency spreading is disabled relative tothe first mode of symbol transmission and at the same particulartransmission rate if the wireless channel characteristic is below thethreshold level. A symbol may be transmitted while disabling at leastone of time spreading and frequency spreading (which is enabled in thefirst mode of symbol transmission) if the second mode of symboltransmission is selected.

Time spreading may include transmitting different versions of the samesymbol at a plurality of different times. Frequency spreading mayinclude concurrently transmitting the same symbol over differentfrequencies.

For a first data transmission rate, the first mode of symboltransmission may utilize time spreading but the second mode of symboltransmission disables time spreading. For a second data transmissionrate, the first mode of symbol transmission may utilizes both timespreading and frequency spreading but the second mode of symboltransmission disables at least one of time spreading and frequencyspreading.\

Prior to transmission, the transmitter may convert a symbol from adigital representation to an analog signal for transmission over anultra wideband wireless channel associated with the wireless channelcharacteristic.

The transmitter may send an indicator to the receiver device that atleast one of time spreading and frequency spreading is disabled.

The transmitter may be compliant with the ultra wideband EuropeanComputer Manufacturers Association (ECMA) 368 standard.

The transmitter and/or method may also reduce one of either the dutycycle or speed of an inverse Fast Fourier Transform module during thesecond mode of symbol transmission, where a (data) transmission ratefrom the wireless transmitter device remains the same despite thereduction of duty cycle or speed of the inverse Fast Fourier Transformmodule.

According to a time repetition scheme during the second mode of symboltransmission, the transmitter and/or method may: (a) modulate a symbolinto a first frequency using an inverse Fast Fourier Transform module;(b) store the modulated symbol; (c) transmit the modulated symbol to thereceiver device on a symbol transmission period; (d) retransmit thestored modulated symbol to the receiver device during other symboltransmission periods; and/or (e) disable the inverse Fast FourierTransform module during the other symbol transmission periods whenretransmitting the stored modulated symbol to conserve power.

According to a time gating scheme during the second mode of symboltransmission, the transmitter and/or method may: (a) generate a symbolfor transmission using an inverse Fast Fourier Transform module; (b)transmit the symbol just once to a receiver device using greatertransmission power than used in the first mode of symbol transmission totransmit symbols; and/or (c) disable the inverse Fast Fourier Transformmodule during time periods when the symbol would have otherwise beenretransmitted in the first mode of symbol transmission.

According to one feature, a receiver device and/or method are providedfor achieving power conservation. In one example, the receiver mayreceive an indicator from a transmitter device indicating at least oneof two modes of symbol transmission. These modes of transmission mayinclude a first mode and a second mode. In the first mode of symboltransmission, the receiver device may enable at least one of timespreading and frequency spreading for a particular transmission rate. Inthe second mode of symbol transmission, the receiver device may disableat least one of time spreading and frequency spreading relative to thefirst mode of symbol transmission and the same particular transmissionrate. If operating in the second mode, the receiver may reduce one ofeither the duty cycle or processing speed of a Fast Fourier Transformmodule relative to the first mode for the same particular transmissionrate.

Time spreading may include the transmission of the same symbol at aplurality of different times over different frequencies. Frequencyspreading may include the concurrent transmission of the same symbolover different frequencies.

For a first data transmission rate, the first mode of symboltransmission may utilize time spreading but the second mode of symboltransmission disables time spreading. For a second data transmissionrate, the first mode of symbol transmission may utilize both timespreading and frequency spreading but the second mode of symboltransmission disables at least one of time spreading and frequencyspreading.

The receiver and/or method may also include (a) receiving a symboltransmitted according to the first mode, if the first mode is indicated;and/or (b) receiving a symbol transmitted according to the second mode,if the second mode is indicated.

The receiver device may include a receiver chain that includes a FastFourier Transform module.

The receiver device is compliant with the ultra wideband EuropeanComputer Manufacturers Association (ECMA) 368 standard.

According to a time repetition scheme when using the second mode forsymbol reception, the receiver device may be adapted to: (a) receive thesame version of a symbol over the same frequency over a plurality ofsymbol transmission periods; (b) accumulate the received versions of thesymbol; (c) disable the Fast Fourier Transform until all versions of thesymbol have been received to conserve power; and/or (d) process theaccumulated symbol using the Fast Fourier Transform module.

According to a time repetition scheme when using the second mode forsymbol reception, the receiver device may be adapted to: (a) receive asymbol just once instead of a plurality of times over a plurality ofsymbol transmission periods as in the first mode, wherein the symbol istransmitted at a higher power than used in the first mode for the samesymbol transmission; and/or (b) disable the Fast Fourier Transformmodule during time periods when the symbol would have otherwise beenretransmitted in the first mode of symbol transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, nature, and advantages of the present aspects may becomemore apparent from the detailed description set forth below when takenin conjunction with the drawings in which like reference charactersidentify correspondingly throughout.

FIG. 1 is a conceptual illustration of an example of a wireless networkin which a mobile access terminal implementing ultra widebandcommunications may operate.

FIG. 2 illustrates an example of an ECMA 368 Ultra-Wideband (UWB)frequency spectrum for Multi-band Orthogonal Frequency DivisionMultiplexing (MB-OFDM).

FIG. 3 is a chart illustrating example of the time-frequency code (TFC)patterns for ten TF codes which spread data symbols over all availablebands in a band group.

FIG. 4 is a chart illustrating an example of the PHY layerchannelization scheme of the time-frequency codes of FIG. 3.

FIG. 5 illustrates an example of how a plurality of symbols may betransmitted by a UWB compliant device.

FIG. 6 illustrates an example of a physical layer (PHY) frame structureof a UWB communication network.

FIG. 7 is a table illustrating an example of modulation parameters foran ECMA 368 compliant transceiver.

FIG. 8 is a diagram illustrating how a symbol may be spread across aplurality of frequencies.

FIG. 9 is a diagram illustrating how a symbol may be spread across time.

FIG. 10 is a block diagram of an access terminal having a low-powerconsumption UWB communication interface.

FIG. 11 is a block diagram illustrating an example of a wirelesstransmitter that may be adapted for low-power consumption.

FIG. 12 is a block diagram illustrating a more detailed example of atransmitter device.

FIG. 13 illustrates an example of how a symbol is sent just once, ratherthan a plurality of times, but at a higher transmission power.

FIG. 14 illustrates how time gating may achieve power reduction byturning off components of transmitter chain when implementing timegating.

FIG. 15 illustrates how the same first symbol is transmitted on the samefrequency a plurality of times instead of using different frequencies.

FIG. 16 is a block diagram illustrating a low-power transmitter that maybe adapted to perform power-conservation.

FIG. 17 is a block diagram illustrating how power conservation may beachieved using time gating on a transmitter device having multiple modesof operation.

FIG. 18 is a block diagram illustrating how power conservation may beachieved using time repetition on a transmitter device having multiplemodes of operation.

FIG. 19 illustrates a method for reducing power consumption in wirelesstransmitter device.

FIG. 20 illustrates an example of a method for performing time gating ona transmitter.

FIG. 21 illustrates an example of a method for performing timerepetition on a transmitter.

FIG. 22 is a block diagram illustrating an example of a wirelessreceiver that may be adapted for low-power consumption.

FIG. 23 is a block diagram illustrating a more detailed example of areceiver device.

FIG. 24 is a block diagram illustrating how a receiver may operate whentime gating is used by a transmitter.

FIG. 25 is a block diagram illustrating how a receiver may operate whentime repetition is used by a transmitter.

FIG. 26 is a block diagram illustrating a low-power receiver that may beadapted to perform power-conservation.

FIG. 27 is a block diagram illustrating how power conservation may beachieved using time repetition on a receiver device having multiplemodes of operation.

FIG. 28 illustrates a method for reducing power consumption in wirelessreceiver device.

DETAILED DESCRIPTION

In the following description, specific details are given to provide athorough understanding of the embodiments. However, it will beunderstood by one of ordinary skill in the art that the embodiments maybe practiced without these specific detail. For example, circuits may beshown in block diagrams in order not to obscure the embodiments inunnecessary detail. In other instances, well-known circuits, structuresand techniques may be shown in detail in order not to obscure theembodiments.

In the following description, certain terminology is used to describecertain features. The terms “access terminal”, “communication device”and “UWB radio” may be interchangeably used to refer to a mobile device,mobile phone, wireless terminal, access terminal and/or other types ofmobile or fixed communication apparatus capable of communicating over anUWB wireless network or system. The terms “wireless network” and“communication system” may be interchangeably used to refer to a shortrange communication system, such as a Multi-band Orthogonal FrequencyDivision Multiplexing (OFDM) UWB system. The term “transceiver” refersto a communication interface having both transmitter and receivercapabilities.

Overview

At least two solutions are proposed to reduce power consumption of UWBtransmitters/receivers, allowing them to be implemented on mobilecommunication devices with limited power sources. In one example, thesefeatures may be applicable to transmitters/receivers operating accordingto a ECMA-368 UWB standard at data rates 53.3, 80, 106.7, 160 and/or 200Mbps.

Processing at the UWB transmitter and receiver may be reduced by takingadvantage of the fact that there is both time spreading and frequencyspreading when operating at in 53.3 and 80 Mbps modes and time spreadingwhen operating in 106.7, 160 and 200 Mbps modes. In the ECMA-368 UWBstandard, time and frequency spreading is used to provide diversity,thereby improving transmissions. However, the use of time and/orfrequency spreading means that every symbol (e.g., OFDM symbol) isprocessed individually. Reduction of power consumption may be achievedby reducing the amount of processing performed for each symbol to betransmitted. Additionally, significant power reduction (e.g., powerconservation) is may also be achieved from cycling or reducing the speedof the IFFT, FFT, encoding and decoding blocks or modules. Consequently,it is recognized that the diversity gain provided by time and frequencyspreading can be traded off in order to lower power consumption. Thispower conservation mode of operation can be turned On when there isenough margin in the link budget. In other scenarios, the loss in thediversity gain may be minimal due to the usage models and the nature ofthe UWB channels.

According to one feature, if channel conditions indicate that timeand/or frequency spreading are unnecessary for transmissions, atransmitter may enter into a power-conservation mode of operation inwhich transmissions are performed using a time gating scheme or a timerepetition scheme. In the time gating scheme, symbols are transmittedjust once, rather than a plurality of times, but with increasedtransmission power. Thus, some of the transmitter chain components canbe operated at a lower duty cycle or processing speed to conserve power.In the time repetition scheme, copies of the same symbol are transmitteda plurality of times on the same frequency on different symboltransmission periods. This is in contrast to an approach in which asymbol may be transmitted on the different frequencies on differentsymbol transmission periods. Consequently, the symbol can be generatedjust once and stored for subsequent retransmission, thereby allowingsome of the transmitter chain components can be operated at a lower dutycycle or processing speed to conserve power.

According to another feature, a receiver may receive an indicator from atransmitter indicating a mode of symbol transmission. One mode of symboltransmission may be a power-conservation mode in which time and/orfrequency diversity are sacrificed in favor of lower power consumptionfor the transmitter and/or receiver. The indicator may indicate, forexample, a time gating scheme or a time repetition scheme. In the timegating scheme, a receiver receives a symbol just once but a highertransmission power than normal, allowing the some of the receiver chaincomponents can be operated at a lower duty cycle or processing speed toconserve power. In the time repetition scheme, the copies of a symbolare received on different symbol transmission periods but on the samefrequency. Therefore, the receiver can accumulate the copies of thesymbol in a buffer or accumulator, thereby allowing some of the receiverchain components can be operated at a lower duty cycle or processingspeed to conserve power while the copies of the symbol are beingaccumulated.

UWB Wireless Network

FIG. 1 is a conceptual illustration of an example of a wireless networkin which a mobile access terminal implementing ultra widebandcommunications may operate. A wireless network 100 may include aplurality of mobile access terminals 104 and 106 that operate in an UWBspectrum. In various examples, the wireless network 100 may be apersonal area network (PAN), a wide area network (WAN), etc. In oneexample, the mobile access terminals 104 and 106 may include atransceiver that operates in the ECMA 368 Ultra-Wideband (UWB) frequencyspectrum, e.g., for Multi-band Orthogonal Frequency DivisionMultiplexing (MB-OFDM). In some implementations, one or more of theaccess terminals may be adapted to provide multi-mode operation, where aterminal may communicate over a plurality of different types ofcommunication interfaces. For instance, a multiple-access terminal mayinclude one or more communication interfaces adapted to communicate overcode division multiple access (CDMA) systems, time division multipleaccess (TDMA) systems, frequency division multiple access (FDMA)systems, and/or orthogonal frequency division multiple access (OFDMA)systems, and the like. Such communication interfaces may conform tospecifications, such as, ECMA-368, third generation partnership project(3GPP), long-term evolution (LTE), etc. According to one feature, theaccess terminals 104 and/or 106 may include a low-power consumption UWBcommunication interface.

Introduction—UWB Network Example

Ultra wideband (UWB) may permit high-speed transmission of large amountsof data over a relatively broad range of frequency bands, usingrelatively low power, at a short range. UWB systems have a capacityproportional to their bandwidth and the logarithm of signal-to-noiseratio (SNR). UWB systems may utilize the signal spreading characteristicthat a pulse signal widely spreads in the frequency domain when a veryshort pulse is transmitted in the time domain. Since trains of shortduration pulses are spread to perform communications, UWB systems canshorten the pulse repetition period and lower the transmitted energydensity per unit frequency to a level below the energy density forthermal noise. In UWB systems, transmission frequency bands may bedetermined according to the waveforms of pulses. UWB signal is a form ofspread spectrum and hence provide a degree of protection against fadingeven in the presence of interference. UWB systems may be time-gated,hence may consume less power.

FIG. 2 illustrates an example of an ECMA 368 Ultra-Wideband (UWB)frequency spectrum 202 for Multi-band Orthogonal Frequency DivisionMultiplexing (MB-OFDM). Ultra wideband (UWB) has become a solution forapplications that benefit from relatively high bandwidth, such aswireless file transfer and video streaming. The ECMA-368 Standardspecifies the ultra wideband (UWB) physical layer (PHY) for a wirelesspersonal area network (PAN), utilizing the unlicensed 3,100-10,600 MHzfrequency band, supporting data rates of 53.3 Mb/s, 80 Mb/s, 106.7 Mb/s,160 Mb/s, 200 Mb/s, 320 Mb/s, 400 Mb/s, and 480 Mb/s.

In this example, the UWB spectrum 202 is divided into fourteen (14)bands, each 528 MHz wide, in the spectral range 3.1 GHz to 10.6 GHz.These bands may be further grouped into five band groups. For instance,the first twelve (12) bands may be then grouped into four (4) bandgroups consisting of three (3) bands, and the last two bands are groupedinto a fifth band group. That is, Band Group #1 may include bands 1-3;Band Group #2 may include bands 4-6; Band Group #3 may include bands7-9; Band Group #4 may include bands 10-12; and Band Group #5 mayinclude bands 13-14. By having four adjacent groups of three bands, pathloss at lower frequencies may be less than at higher frequencies, thusthe lower bands may be preferred. Some hardware implementations of UWBphysical layer (PHY) can use only one band group, (typically the lowestband Group #1), but other PHY implementations can use multiple bandgroups. The design of a PHY supporting multiple band groups may besimplified by the fact that Band Groups #1 through #5 all have the samebandwidth. Therefore, the PHY transmitter or receiver can tune to any ofthe first 4 band groups by simply changing a local oscillator frequency.Common filtering and processing before up conversion (at transmitter) orafter down conversion (at receiver) may be applied to a 528 MHz wideband regardless of band group chosen thus reducing circuit complexity.In another embodiment, an additional band Group #6 may be definedcontaining bands 9, 10, and 11.

The ECMA-368 Standard specifies a Multi-Band Orthogonal FrequencyDivision Modulation (MB-OFDM) scheme to transmit information. A total of110 sub-carriers (100 data carriers and 10 guard carriers) are used perband to transmit the information. In addition, 12 pilot subcarriersallow for coherent detection. Frequency-domain spreading (FDS),time-domain spreading (TDS), and forward error correction (FEC) codingare used to vary the data rates. The FEC used is a convolutional codewith coding rates of 1/3, 1/2, 5/8 and 3/4.

Coded bits may be aggregated into groups of 100 or 200 bits each. Pairsof bits within a group may be modulated, using known modulationtechniques such as quadrature phase shift keying (QPSK), onto datatones, typically 100, generally equally spaced in one of the 528 MHzbands. Symbols associated with a unique piconet may be assigned aspecific one of the 6 band groups, and may be further assigned a uniquetime-frequency code within the assigned band group. The band assignedfor successive symbols may either change with time or remains constantaccording to a time frequency code.

Unique logical channels may be defined by using up to ten differenttime-frequency codes (TFC) for each band group. Time-frequency codes maybe hopping patterns used by the ECMA 368 signal. In one example, theremay be three types of patterns. The first type may be Time-FrequencyInterleaved (TFI), and may include signals that hop in various patternsamong the three frequency bands in the band group. The second type wherethe coded is interleaved over two bands in the same band group and isreferred to as two-band TFI or TFI2. The third type may be calledFixed-Frequency Interleaved (FFI), in which the signal may not hop butstays in one frequency band. The length of the TFC code may be n symbols(where n is an integer value), so it is repeated at least several timesduring a packet.

FIG. 3 is a chart 302 illustrating example of the time-frequency code(TFC) patterns for ten TF codes which spread data symbols over allavailable bands in a band group. The code patterns may determine whichof the three (3) (or 2 in the case of Band Group #5) available bands ina band group may be used for successive data symbols from a givenpiconet. For example, given Band Group #1 and examining TFC 1, datasymbols may be transmitted sequentially in band 1, band 2, band 3, band1, band 2, band 3, repeating indefinitely. The same TFC 1 used in bandgroup 2 may transmit data sequentially in band 4, band 5, band 6, band4, band 5, band 6, repeating indefinitely. Each network may be assignedone of the band groups and a unique TFC within that band group.

FIG. 4 is a chart 402 illustrating an example of the PHY layerchannelization scheme of the TFCs of FIG. 3. The chart 402 shows themapping of the medium access control (MAC) Channel Number to PHY BandGroup and TF Code as well as the TFCs and corresponding repeatingsequence of band numbers for successive data symbols, each TFC may benon-varying as a function of time. Unique logical channels may bedefined by using up to 10 different TFC codes for each band group. Thechannel number may take on values from 0-255 (decimals).

In one embodiment, channel numbers 9-15 may be mandatory. Channels usingTFCs 1-4 may be time-frequency interleaved (TFI) channels, as describedabove, and those using TFCs 5-7 may be fixed-frequency interleaved (FFI)channels, described above. As a result of the large number of channelsthat the acquiring device may need to search through in order to findthe correct TFC, UWB initial acquisition may be very slow.

FIG. 5 illustrates an example of how a plurality of symbols may betransmitted by a UWB compliant device. Each symbol 502 may include anOFDM symbol portion 504 and a Zero-Padded Suffix portion 506. Thesymbols may be transmitted using a over a plurality of frequenciesaccording to a time-frequency code (e.g., illustrated in FIGS. 3 and 4).In this example, three frequency bands (Band A, Band B, and Band C) areused for symbol transmissions, where a first symbol 51 is transmitted ata center frequency for a first band Band A, the second symbol S2 istransmitted over a second band Band B, the third symbol S3 istransmitted over a third band Band C, the fourth symbol S4 istransmitted over the first band Band A, the fifth symbol S5 istransmitted over the second band Band B, the sixth symbol S6 istransmitted over the third band Band C, and so on. For instance, if TFC#1 in FIG. 3 is used for transmissions, Band A is Band #1 (FIG. 2), BandB is Band #2 (FIG. 2), and Band C is Band #3 (FIG. 2).

FIG. 6 illustrates an example of a physical layer (PHY) frame structureof a UWB communication network. As described above, a physical layerconvergence protocol (PLCP) may provide a method to convert a servicedata unit (SDU) into a protocol data unit (PDU). The PLCP PDU (PPDU) maycomprise three components: the PLCP preamble 602, the PLCP header 604and the PLCP SDU (PSDU) 606. The PLCP header 604 may comprise a physicalheader (“PHY header”), tail bits or tails symbols (“TS”), a media accesscontrol header (“MAC header”), a header check sequence (“HCS”), and padbits or stuff bits (“SB”). The PSDU 606 may comprise the frame payload,a data SNR+ frame check sequence (“FCS”), tail bits or tail symbols(“TS”) and pad bits or stuff bits (“SB”).

The preamble 602 may comprise two portions, a time-domain portion forpacket/frame synchronization followed by a frequency domain portion forchannel estimation. The preamble 602 may be used for synchronizationduring a transmitting/receiving process, carrier offset compensation andequalization of received signals. A unique preamble sequence may beassigned to each TFC. The PHY header may be used to show information,such as a scrambling code, data rate of an MAC frame and data length.The MAC header may be used to show a frame adjusting signal, a networkidentifier (“PNID”), a destination identifier (“DestID”), a sourceidentifier (“SrcID”), fragmentation control information and stream indexinformation.

The HCS may be used to detect errors occurring in the PHY header and theMAC header. In the data+FCS, a data field may be used to transmit datawith its encryption data. The FCS field may be used for error detectionin the data which is being transmitted. Bits in the SB may be a type ofdummy bits inserted to generate the data+FCS in a size that may be aninteger multiple of the symbol size applied to the desired data rate. Asa result, when the size of the data+FCS is an integer multiple of thesymbol size applied to the desired data rate, the SB may not need to beinserted.

FIG. 7 is a table illustrating an example of modulation parameters foran ECMA 368 compliant transceiver. In this example, it can be observedthat for data rates 53.3 and 80 Mbps both time and frequency spreadingis used, while for data rates 106.7, 160 and 200 Mbps only timespreading is used. Frequency-domain spreading (FDS), time-domainspreading (TDS), and forward error correction (FEC) coding are used tovary the data rates. The FEC used is a convolutional code with codingrates of 1/3, 1/2, 5/8 and 3/4. For data rates of 200 Mb/s and lower,the binary data is mapped onto a QPSK constellation. For data rates of320 Mb/s and higher, the binary data shall be mapped onto amulti-dimensional constellation using a dual-carrier modulation (DCM)technique.

The coded data may be spread using a time-frequency code (TFC), asillustrated in FIGS. 3 and 4. The ECMA-368 Standard specifies two typesof time-frequency codes (TFCs): one where the coded information isinterleaved over three bands, referred to as Time-Frequency Interleaving(TFI); and, one where the coded information is transmitted on a singleband, referred to as Fixed Frequency Interleaving (FFI). Within each ofthe first four band groups, four time-frequency codes using TFI andthree time frequency codes using FFI are defined; thereby, providingsupport for up to seven channels per band. For the fifth band group, twotime-frequency codes using FFI are defined. This ECMA-368 Standardspecifies 30 channels in total.

Frequency Spreading—Principle

FIG. 8 is a diagram illustrating how a symbol may be spread across aplurality of frequencies. In order to make transmissions lesssusceptible to noise and interference, frequency spreading may beemployed in which a symbol is repeated across a plurality of frequenciesfor transmission. For instance, in FIG. 8 a symbol s1 is transmitted attime t0 (or a given transmission time slot) over frequencies (orfrequency bands) f_(a), f_(b), f_(e), and f_(d). That is, a firstversion s1 _(a) of the symbol s1 is transmitted on a first frequencyf_(a), a second version s1 _(b) of the symbol s1 is transmitted on asecond frequency f_(b), a third version s1 _(c) of the symbol s1 istransmitted on a third frequency f_(e), and a fourth version s1 _(d) ofthe symbol s1 is transmitted on a fourth frequency f_(d). Such frequencyspreading may occur within a frequency band (e.g., Bands 1, 2, 3 . . .14 of FIG. 2) and/or across a plurality of frequency bands within a bandgroup (e.g., Band Groups 1, 2 . . . 6, of FIG. 3). Note that, ascontemplated herein, “frequency spreading” may include other schemes,including frequency spreading schemes for OFDM transmission systems.

While frequency spreading helps improve spectrum diversity for eachtransmitted symbol, it also means that a symbol is transmitted aplurality of times, resulting in more power consumption for thetransmitter device. Likewise, the receiver device may consume more poweras it has to receive and demodulate the same symbol a plurality oftimes.

In one example, such frequency spreading may be implemented by afrequency spreader 1208 of the transmitter 1202 of FIG. 12. Likewise,frequency de-spreading may be implemented by a frequency de-spreader2134 of the receiver of FIG. 21.

In the ECMA 368 standard, frequency spreading is implemented where acoded bit or symbol is concurrently sent on four different tones (e.g.,frequencies or frequency bands) for data rates 53.3 and 80 Mbps.Similarly, the same coded bit or symbol is sent concurrently twodifferent tones for data rates 106.7, 160, and 200 Mbps.

According to one feature, under certain circumstances, frequencyspreading may be switched Off so as to conserve power at the transmitterand/or receiver. This also allows cycling certain transmitter/receivercomponents to further conserve power.

Time Spreading—Principle

FIG. 9 is a diagram illustrating how a symbol may be spread across time.In order to make transmissions less susceptible to noise andinterference, frequency spreading may be employed in which a symbol isrepeated at different transmission times and at different frequencies(or frequency bands). For instance, at time t0, a first symbol s1 istransmitted. Then, at a later time t0+i when a second symbol s2 is beingtransmitted, the first symbol s1 is again transmitted but at a secondfrequency f_(b). At a later time t0+2i when a third symbol s3 is beingtransmitted, the first symbol s1 is again transmitted but at a thirdfrequency f_(e). Similarly, at a later time t0+3i when a fourth symbols4 is being transmitted, the first symbol s1 is again transmitted but ata fourth frequency f_(d). In this example, the symbol s1 is transmittedusing a transmit power P₀. While time spreading helps improve spectrumdiversity for each transmitted symbol, it also means that a symbol istransmitted a plurality of times, resulting in more power consumptionfor the transmitter device. Likewise, the receiver device may consumemore power as it has to receive and demodulate the same symbol aplurality of times.

In the ECMA 368 standard, time spreading is implemented where a codedbit or symbol is sent four times (e.g., on different frequencies orfrequency bands) for data rates 53.3 and 80 Mbps. Similarly, the samecoded bit or symbol is sent two times for data rates 106.7, 160, and 200Mbps.

According to one feature, under certain circumstances, time spreadingmay be switched off so as to conserve power at the transmitter and/orreceiver. This also allows cycling certain transmitter/receivercomponents to further conserve power.

Note that the symbols illustrated in FIGS. 8 and 9 may be OFDM symbolsthat can be represented as complex symbols having a real and imaginarycomponents. Such details are omitted for simplicity purposes.

Also note that where both frequency and time spreading are implementedin the ECMA 368 Standard, a coded bit or symbol may be sent four timeson four different tones for data rates 53.3 and 80 Mbps and twice on twodifferent tones for data rates 106.7, 160 and 200 Mbps.

Example Access Terminal

FIG. 10 is a block diagram of an access terminal having a low-powerconsumption UWB communication interface. In this example, the accessterminal 1002 may include a processing circuit 1004 communicativelycoupled to a network communication interface 1006 through with theaccess terminal 1002 can communicate with a wireless network 1008. Thenetwork communication interface 1006 maybe a transceiver that includes atransmitter 1010 and/or a receiver 1012 that are adapted to communicateover a UWB wireless network. In some embodiments, the access terminal1002 may also include additional network communication interfaces thatare adapted to communicate over different types of wireless networks.According to various examples, the access terminal 1002 may be a mobiledevice, mobile phone, wireless terminal, personal communication device,a mobile computing device, a mobile digital media player, and/or othertypes of mobile or fixed communication devices.

The access terminal 1002 may be powered by a power source 1014, e.g.,rechargeable battery. In order to extend the operating life of the powersource, e.g., extend operating time in between recharges, the networkcommunication interface 1006 may include one or more features to reducepower consumption for UWB transmissions/reception.

Low-Power Transmitter

FIG. 11 is a block diagram illustrating an example of a wirelesstransmitter that may be adapted for low-power consumption. Thetransmitter 1102 may include a digital baseband processor 1104 thatprocesses input data 1110. A radio modulator 1106 may receive theprocessed input data from the digital baseband processor 1104 andmodulates it into output data for wireless transmission over an antenna1108. The antenna 1108 may transmit the output data 1112 over a wirelessnetwork (e.g., a UWB network).

FIG. 12 is a block diagram illustrating a more detailed example of atransmitter device. In one example, one or more of the componentsillustrated in FIG. 12 may be part of the baseband processor 1104 and/orradio modulator 1106 of FIG. 11.

In the transmitter 1202, scrambled input data (e.g., data fortransmission) is passed from a convolutional encoder and interleaver1204, to a constellation mapper 1206, to a frequency spreader 1208(which spreads the data in the frequency domain) and to apilot/null/guard tone inserter 1210 to generate a coded symbol stream.

A serial-to-parallel converter 1212 then converts the coded symbolstream to a plurality of parallel streams that are processed by aninverse Fast Fourier Transform (IFFT) module 1214 to convert the codedsymbols from the time domain to the frequency domain. Aparallel-to-serial converter 1216 then converts the parallel datastreams to a serial data stream of OFDM symbols. Note that, in thisexample, a zero padded suffix (ZPS) is appended to the OFDM symbol. TheZPS may be 37 bits long and appended to the 128 point data to obtain atotal of 165 bits which are converted by the parallel-to-serialconverter 1216. A time spreader 1218 then spreads the serial data in thetime domain and a digital-to-analog converter 1120 converts the datainto one or more analog signals. A transmitter analog filter 1122 isused to remove extraneous frequencies and the resulting analog signal ismodulated by a transmit frequency from a frequency synthesizer 1124 fortransmission over an antenna 1126.

Under typical operation, the frequency spreader 1208 is repeating thesame symbol a plurality of times (repetition) across differentfrequencies. For instance, in the ECMA 368 Standard, a coded bit orsymbol is sent four times on four different tones for data rates 53.3and 80 Mbps and twice on two different tones for data rates 106.7, 160and 200 Mbps. This causes the IFFT Module 1214 and digital-to-analogconverter 1220 to operate very fast and consume a lot of power.Likewise, in the modes where the time spreader 1218 is operational, itcauses the same symbol to be repeated at different times, causingadditional power consumption to the transmitter and receiver devices.

Under certain circumstances, it is possible to reduce the powerconsumption of the transmitter 1202 by trading off frequency diversityand/or time diversity. That is, rather than operating the transmitter1202 in a conventional manner (e.g., having full frequency and/or timediversity), the frequency and/or time spreading may be reduced oreliminated (under certain circumstances) to lower power consumption. Forexample, in situations where channel conditions are relatively good(e.g., a minimum level of signal strength is present and/or noise orinterference is below a threshold level), the use of frequency and/ortime spreading is wasteful of the limited power resources. Consequently,one feature provides for modifying the operation of the transmitter (andreceiver) if it is determined that the communication channel hasinterference and/or noise below a particular threshold. Under suchcircumstances, frequency and/or time spreading may be eliminated orreduced without significantly impacting transmissions (e.g., withoutimpacting the data transmission rate).

Two approaches, referred to as time gating and symbol repetition, aredescribed below which may result in reduced power consumption by atransmitter (and receiver) when channel conditions allow eliminatingand/or reducing frequency and/or time diversity (spreading). This powerconservation may be achieved while still maintaining the same effectivedata transmission rate from a transmitter to a receiver.

According to an example of time gating operational on a transmitter, thefrequency spreader 1208 and/or time spreader 1218 may be turned Off ornon-operational (not cycled) while the DAC 1220, TX analog filter 1222,the frequency synthesizer 1224, and/or the antenna 1226 may be cycledOff/On. Meanwhile, the Pilot/Null/Guard Tones inserter 1210, theserial-to-parallel converter 1212, the IFFT module 1214, and/or theparallel-to-serial converter 1216 may be operated at a lower speed orcycled Off/On (e.g., lower duty cycle). In some instances, the preferredapproach may be to operate these devices at a lower speed.

According to an example of time repetition operational on a transmitter,the frequency spreader 1208 and/or time spreader 1218 may be turned Offor non-operational (not cycled). Meanwhile, the Pilot/Null/Guard Tonesinserter 1210, the serial-to-parallel converter 1212, the IFFT module1214, and/or the parallel-to-serial converter 1216 may be cycled Off/On(e.g., changing the duty cycle) or operated at a lower speed. In someinstances, the preferred approach may be to operate these devices at alower speed.

Time Gating—Alternative to Time Spreading

According to a first feature, instead of sending a symbol a plurality oftimes (e.g., two or four times), the symbol is sent just once using morepower. That is, in the ECMA-368 Standard, one symbol (or coded bit) maybe sent four times on four different tones for data rates 53.3 and 80Mbps and twice on two different tones for data rates 106.7, 160 and 200Mbps.

FIG. 13 illustrates an example of how a symbol is sent just once, ratherthan a plurality of times, but at a higher transmission power. Incomparison to FIG. 9, where symbol s1 is sent at four different timesand frequencies, in this approach the symbol s1 is sent just once butwith more power. Consequently, the symbol s1 is not retransmitted onsubsequent time periods t0+i, t0+2i, and t0+3i (as in FIG. 9) butinstead is transmitted only once (during the time period t0). Accordingto one implementation, the increase in transmission power isproportional to the number of times the symbol would have been repeated.For example, in the ECMA-368 standard the symbol s1 may be sent fourtimes at with a transmission power P₀. However, according to thealternative approach herein described, the same symbol s1 is sent justonce but at four times the power P₀ (or 4×P₀). Unlike the conventionalapproach, the symbol s1 is not repeated in subsequent transmission timeslots.

For a transmitter compliant with the ECMA 368 standard, for data rates53.3 and 80 Mbps the symbol is transmitted just once (instead of fourtimes) at four times the original power. Similarly, for data rates106.7, 160, and 200 Mbps the symbol is sent only once (instead of twotimes) at twice the original power.

Since the symbol s1 is transmitted just once (rather than multipletimes), several transmitter components may be cycled Off during thosetimes when it is no longer being transmitted. For instance, in FIG. 12,the IFFT module 1214 and/or the components (e.g., digital-to-analogconverter 1220, TX analog filter 1222, etc.) after the IFFT module 1214in the transmitter chain may be turned Off.

FIG. 14 illustrates how time gating may achieve power reduction byturning off components of transmitter chain when implementing timegating. In the typical approach, a symbol s1 is transmitted four times(shown as s1 _(a), s1 _(b), s1 _(c), s1 _(d)) at different times.However, by transmitting the symbol s1 with no repetition but withgreater power, some transmitter chain components (such as the IFFTmodule 1214, parallel-to-serial converter 1216, time spreader 1218,digital-to-analog converter 1220, and TX analog filter 1222) may becycled Off.

According to one approach, the IFFT module 1214 may run at the samespeed as before but may be cycled On/Off so as to conserve power duringtimes when the symbol is not longer being transmitted. For example, forthe ECMA 368 standard, at data rates 53.3 and 80 Mbps (where a symbol istypically transmitted four different times), the IFFT module 1214 mayonly be turned On one fourth of the time (as illustrated in FIG. 14)during which the symbol is transmitted just once at four times theoriginal power. That is, the IFFT module 1214 is On for one symboltransmission and Off for the following three symbol transmissions.Similarly, at data rates 106.7, 160, and 200 Mbps (where a symbol istypically transmitted two different times), the IFFT module 1214 may beturned On half of the time during which the symbol is transmitted justonce at twice the original power. That is, the IFFT module 1214 is Onfor one symbol transmission and Off for the next symbol transmission.

According to a second approach, the IFFT module 1214 may run at a slowerspeed than the conventional implementation to conserve power. Forexample, for the ECMA 368 standard, at data rates 53.3 and 80 Mbps(where a symbol is typically transmitted four different times within atime period), the IFFT module 1214 may run at one fourth the originalspeed for the entire time period to transmit a symbol just once. Thatis, the IFFT module 1214 is On for the entire time period but is run atonly one quarter the original speed, thereby conserving power.Similarly, at data rates 106.7, 160, and 200 Mbps (where a symbol istypically transmitted two different times within a time period), theIFFT module 1214 may be run at half its original speed for the entiretime period to transmit a symbol just once. That is, the IFFT module1214 is On for the entire time period but is run at only half theoriginal speed, thereby conserving power.

Time Repetition—Alternative to Frequency Spreading

According to a second feature, instead of sending a symbol a pluralityof times but on different frequencies (as in frequency spreading of FIG.8), the symbol is sent on the same frequency or tone each time. In theECMA-368 Standard, one symbol (or coded bit) is sent four times on fourdifferent tones for data rates 53.3 and 80 Mbps and twice on twodifferent tones for data rates 106.7, 160 and 200 Mbps. Thus, each timethe symbol is to be sent, it is modulated into a different frequency ortone (as illustrated in FIGS. 8 and 9). In the present approach, thesymbol is modulated into frequency just once (at a first frequency ortone), stored, and sent a plurality of times. By storing the symbol, theIFFT module 1214 can avoid generating the symbol each time.Consequently, either the duty cycle or the processing speed of the IFFTmodule 1214 can be reduced, thereby conserving power. Additionally, theFrequency Spreader module 1208 and/or Time Spreading module 1218 areturned Off.

FIG. 15 illustrates how the same first symbol s1 is transmitted on thesame frequency f_(a) a plurality of times instead of using differentfrequencies. In this example, the first symbol is transmitted just onceduring the time periods t0, t0+i, t0+2i, and t0+3i and on the samefrequency f_(a).

In this approach, one symbol (e.g., OFDM symbol) is generated by adigital baseband module at the transmitter and the output of the IFFT isstored while it is processed by the analog and RF components to betransmitted at time t0 as the current symbol. Then, the stored output ofthe IFFT (e.g., the stored symbol) is repeatedly processed in the sameway by the analog and RF components to be transmitted in subsequenttransmission periods. For instance, for data rates of 53.3 and 80 Mbps,the stored symbol is transmitted three more times. For data rates of106.7, 160, and 200 Mbps, the stored symbol is transmitted one moretime. Therefore, the frequency spreader 1208 and IFFT module 1214 may beturned Off for three symbol periods for 53.3 and 80 Mbps and one symbolperiod for 106.7, 160 and 200 Mbps. Another option is for the IFFTmodule 1214 to run at one fourth of the speed for data rates 53.3 and 80Mbps and half of the speed for data rates 106.7, 160 and 200 Mbps.

In one example, the time gating and time repetition schemes describedherein are exclusive of each other such that they may not beconcurrently executed. Note that, these techniques may co-exist within atransmitter or receiver but only one may be implemented at any onemoment.

Example Low-Power Transmitter

FIG. 16 is a block diagram illustrating a low-power transmitter that maybe adapted to perform power-conservation. In this block diagram, severaltransmitter components may have been omitted or combined for purposes ofclarity. However, it should be understood that additional devices may bepart of the transmitter 1602 without deviating from its novelty. Thetransmitter 1602 may include a transmitter chain 1604, a channelmonitoring module 1606 and/or an antenna 1608. The channel monitoringmodule 1606 may be adapted to monitor a transmission channel (e.g.,assigned frequency band or group) to determine one or more wirelesschannel characteristics such as desired signal strength, channel noise,noise floor, and/or interference. If the wireless channel characteristic(e.g., desired signal strength, channel noise, noise floor,interference, etc.) is below an acceptable threshold level, thetransmitter 1602 may enter into a power conservation mode in whichfrequency and/or time diversity are sacrificed in exchange for utilizingless power during transmissions. That is, in a first (typical) mode ofoperation, the transmitter 1602 may employ frequency diversity (e.g.,frequency spreading) and/or time diversity (e.g., time spreading) fromtransmissions. However, if channel conditions are below an acceptablethreshold level (e.g., noise or interference are relatively low), thenthe transmitter may enter into a second mode of operation (e.g., a powerconservation mode), in which transmissions still occur but with lesserfrequency and/or timing diversity.

The transmitter chain 1604 may include an encoder/interleaver/mapper1604 that receives input data 1610, processes the input data (e.g., asymbol or plurality of symbols), and passes it to a frequency spreader1615. In a first mode of operation, the frequency spreader 1615 mayapply frequency diversity to a symbol in the input data by concurrentlytransmitting the same symbol on different frequencies, frequency bands,or tones. The symbol from the frequency spreader 1615 then passes to anIFFT Module 1616 where it is transformed in the frequency domain and atime spreader 1618 where the symbol is spread in the time domain toprovide time diversity. A digital-to-analog converter (DAC) 1620 thenconverts the digital symbol into an analog signal. An amplifier 1622 mayamplify the signal power for the output signal from the DAC 1620. One ormore Radio Frequency (RF) Devices 1624 (e.g., filters, synthesizers,etc.) may process the output signal from the amplifier 1622 andtransmits it via the antennal 1608.

If the channel monitoring module 1606 has determined that the wirelesschannel characteristics or conditions are below an acceptable thresholdlevel, then the transmitter may enter into a second mode of operation.In this second mode of operation, frequency and/or timing diversity maybe reduced and/or eliminated for the sake of power conservation. In oneexample, where the transmitter is a UWB transmitter, the nature of theUWB channel and lack of noise or interference may allow dispensing withtime and/or frequency diversity without significantly affectingtransmissions.

In one implementation, the transmitter 1602 may implement time gating(as previously described) during the second mode of operation. That is,rather than transmitting the same symbol a plurality of times with atransmit power of P₀ on different time periods (as in FIG. 9), timegating transmits the symbol just once at a higher transmit power. In oneexample, the transmission power may be directly proportional to thenumber of times the symbol would have otherwise been transmitted. Forexample, if a symbol would have normally been transmitted four times,then the new transmit power for the single symbol is 4×P₀. Thus, eventhough time and frequency diversity are sacrificed, the single symbolthat is transmitted is more likely to be correctly received since it hasa higher transmit power. However, because the IFFT module 1616 (andpossibly the frequency spreader 1615 and/or time spreader 1616) is shutoff, the DAC 1620 may be cycled Off during the time in which the symbolis no longer repeated. To achieve this, the amplifier 1622 may beadapted so that it increases its transmit power when operating in thissecond mode of operation.

In another implementation, the transmitter 1602 may instead implementtime repetition (as previously described) during the second mode ofoperation. That is, rather than transmitting the same symbol a pluralityof times on different frequencies during different time periods (asillustrated in FIG. 9), the same symbol is generated just once, storedin a symbol storage 1617, and transmitted a plurality of times on thesame frequency (as illustrated in FIG. 15). Note that once the symbol isstored in the symbol storage 1617, the frequency spreader 1615 and/ortime spreader 1618 may be powered Off (not cycled Off) since they arenot needed to generate the same symbol on different frequencies.Meanwhile, the IFFT module 1616 may be cycled Off/On (e.g., change induty cycle) or it may be operated at a lower speed.

Note that the channel monitoring module 1606 may continuously,periodically, or regularly monitor the channel characteristics orconditions to determine if a change has occurred. If the channelcharacteristics are above a threshold level, then the transmitter 1602may switch back to the first mode of operation. Also, in order toindicate to a receiver that the transmitter is transmitting dataaccording to a second mode of operation, the transmitter may send a modeindicator to the receiver.

In some modes of operation, the transmitter 1602 may be adapted toimplement both of time gating and time repetition schemes though not atthe same time. That is, under certain channel conditions time gating maybe selected, while in other channel conditions time repetition may beselected.

Consequently, a wireless transmitter device is provided a channelmonitoring module and a transmitter chain. The channel monitoring modulemay be adapted to determine a wireless channel characteristic (e.g.,desired signal strength, channel noise or interference) between thetransmitter device and a receiver device. The transmitter chain mayinclude an inverse Fast Fourier Transform module and at least one of atime spreader and frequency spreader. The transmitter chain may beadapted to: (1) select a first mode of symbol transmission in which atleast one of time spreading and frequency spreading is enabled at aparticular transmission rate if the wireless channel characteristic isabove a threshold level; and/or (2) select a second mode of symboltransmission in which at least one of time spreading and frequencyspreading is disabled relative to the first mode of symbol transmissionand at the same particular transmission rate if the wireless channelcharacteristic is below the threshold level. That is, for a first datatransmission rate (e.g., 106.7, 160, or 200 Mbps) the first mode ofsymbol transmission utilizes time spreading but the second mode ofsymbol transmission disables time spreading. Similarly, for a seconddata transmission rate (e.g., 53.3 or 80.0 Mbps) the first mode ofsymbol transmission utilizes both time spreading and frequency spreadingbut the second mode of symbol transmission disables at least one of timespreading and frequency spreading.

The transmitter chain may be further adapted to reduce one of either theduty cycle or speed of the inverse Fast Fourier Transform module if atleast one of the time spreader and the frequency spreader are disabled,wherein a transmission rate from the wireless transmitter device remainsthe same despite the reduction of duty cycle or speed of the inverseFast Fourier Transform module. The transmitter chain may be furtheradapted to convert a symbol from a digital representation to an analogsignal for transmission over an ultra wideband wireless channelassociated with the wireless channel characteristic. The transmitterchain may be further adapted to send an indicator to the receiver devicethat at least one of time spreader and frequency spreader are disabled.

According to some implementations, the time repetition and time gatingmay be performed when a transmitter chain is implementing QuadraturePhase Shift Keying (QPSK) modulation but not when it is implementingDual Carrier Modulation (DCM).

FIG. 17 is a block diagram illustrating how power conservation may beachieved using time gating on a transmitter device having multiple modesof operation. The transmitter chain may include an encoder/interleaver1702, a frequency domain spreader (FDS) 1704, an inverse Fast FourierTransform module (IFFT) 1706, a time domain spreader (TDS) 1708, adigital-to-analog converter (DAC) 1710, an amplifier 1712, other radiofrequency transmission devices 1714, and an antenna 1718. A modeselector 1716 may control the operation of one or more of thetransmitter chain components by turning them On or Off, adjusting theirduty cycle, and/or slowing their processing speed. Table 1720illustrates an example of how the transmitter chain components may beoperated in a first mode of transmission (regular operation) and in asecond mode of transmission (power conservation operation). The modeselector 1716 may configure the various transmitter chain components asillustrated in table 1720. For instance, during power conservation, theFDS 1704 and/or TDS 1708 may be turned Off, the IFFT module 1706 may becycled Off/On (e.g., reduce its duty cycle) or operated at a slowerspeed, and the DAC 1710 and/or the RF devices 1714 may be gated orcycled (e.g., reduce their duty cycles) to achieve power conservation.Meanwhile, the amplifier 1712 is adjusted to amplify the outgoing signaltransmission; such as 3 dB power amplification for transmission rates of106.7, 160 and 200 Mbps or 6 dB for transmission rates of 53.3 and 80Mbps.

FIG. 18 is a block diagram illustrating how power conservation may beachieved using time repetition on a transmitter device having multiplemodes of operation. For purposes of illustration, a similar transmitterchain as that of FIG. 17 is utilized in this example. The transmitterchain may include an encoder/interleaver 1802, a frequency domainspreader (FDS) 1804, an inverse Fast Fourier Transform module (IFFT)1806, a time domain spreader (TDS) 1808, a digital-to-analog converter(DAC) 1810, an amplifier 1812, other radio frequency transmissiondevices 1814, and an antenna 1818. A mode selector 1816 may control theoperation of one or more of the transmitter chain components by turningthem On or Off, adjusting their duty cycle, and/or slowing theirprocessing speed. Table 1820 illustrates an example of how thetransmitter chain components may be operated in a first mode oftransmission (regular operation) and in a second mode of transmission(power conservation operation). The mode selector 1816 may configure thevarious transmitter chain components as illustrated in table 1820. Forinstance, during power conservation, the FDS 1804 and/or TDS 1808 may beturned Off, the IFFT module 1806 may be cycled Off/On (e.g., reduce itsduty cycle) or operated at a slower speed to achieve power conservation.Meanwhile, the DAC 1810 and/or the RF devices 1814 may be operatednormally and the amplifier 1812 is powered Off (no amplification).

In some implementations, a mode selector may cause a transmitter chainto operate according to a regular mode of operation, a time gating powerconservation mode (as illustrated in FIG. 17), and/or a time repetitionpower conservation mode (as illustrated FIG. 18).

FIG. 19 illustrates a method for reducing power consumption in wirelesstransmitter device. A wireless channel characteristic between thetransmitter device and a receiver device is determined or ascertained1902. A determination may then be made as to whether the channelcharacteristic is less than a threshold level 1904. According to someexamples, the wireless channel characteristic may include ascertainingat least one of: a desired signal strength, channel noise, a noisefloor, or an interference level. The threshold level may be a value thatis consider to acceptable such that time and/or frequency diversity. Forexample, the threshold level may be a desired signal strength threshold,channel noise threshold, a noise floor threshold, an interference levelthreshold, a combination or the inverse thereof.

If the wireless channel characteristic is above a threshold level, afirst mode of transmission is selected in which at least one of timespreading and frequency spreading is enabled at a particulartransmission rate 1906. A symbol may then be transmitted to the receiverdevice using at least one of time spreading and frequency spreading ifthe first mode of symbol transmission is selected 1908. Time spreadingmay include transmitting different versions of the same symbol at aplurality of different times. Frequency spreading may includeconcurrently transmitting the same symbol over different frequencies.

Otherwise, if the wireless channel characteristic is below the thresholdlevel, a second mode of transmission may be selected in which at leastone of time spreading and frequency spreading is disabled relative tothe first mode of symbol transmission and at the same particulartransmission rate 1910. For instance, for a first data transmission rate(e.g., 106.7, 160, or 200 Mbps) the first mode of symbol transmissionmay utilize time spreading but the second mode of symbol transmissionmay disable time spreading. Similarly, for a second data transmissionrate (e.g., 53.3 or 80.0 Mbps) the first mode of symbol transmission mayutilize both time spreading and frequency spreading but the second modeof symbol transmission may disable at least one of time spreading andfrequency spreading.

One of either the duty cycle or speed of an inverse Fast FourierTransform module (in the transmitter chain) may be reduced during thesecond mode of symbol transmission, wherein a transmission rate from thewireless transmitter device remains the same despite the reduction ofduty cycle or speed of the inverse Fast Fourier Transform module 1912.An indicator may also be sent to the receiver device indicating that atleast one of time spreading and frequency spreading are disabled 1914. Asymbol may then be transmitted while disabling at least one of timespreading and frequency spreading which is enabled in the first mode ofsymbol transmission if the second mode of symbol transmission isselected 1916.

Note that, a symbol may be converted from a digital representation to ananalog signal for transmission over an ultra wideband wireless channelassociated with the wireless channel characteristic.

FIG. 20 illustrates an example of a method for performing time gating ona transmitter. This method for time gating may be implemented by: (a)generating an OFDM symbol for transmission using an inverse Fast FourierTransform module 2002; (b) transmitting the OFDM symbol just once to areceiver device using greater transmission power than used in the firstmode of symbol transmission to transmit symbols 2004; and/or (c)disabling the inverse Fast Fourier Transform module during time periodswhen the OFDM symbol would have otherwise been retransmitted in thefirst mode of symbol transmission 2006.

FIG. 21 illustrates an example of a method for performing timerepetition on a transmitter. This method for time repetition may beimplemented by: (a) modulating a symbol into a first frequency using aninverse Fast Fourier Transform module to obtain an OFDM symbol 2102; (b)storing the modulated OFDM symbol 2104; (c) transmitting the modulatedOFDM symbol to the receiver device on a symbol transmission period 2106;(d) retransmitting the stored modulated OFDM symbol to the receiverdevice during other symbol transmission periods 2108; and/or (e)disabling the inverse Fast Fourier Transform module during the othersymbol transmission periods when retransmitting the stored modulatedsymbol to conserve power 2110.

Low-Power Receiver

FIG. 22 is a block diagram illustrating an example of a wirelessreceiver that may be adapted for low-power consumption. The receiver2202 may include a radio demodulator 2206 that receives input data 2210from a network (e.g., a UWB network) over and antenna 2204. The receivedinput data may be processed by a digital baseband processor 2208 toproduce output data 2212.

FIG. 23 is a block diagram illustrating a more detailed example of areceiver device. In one example, one or more of the componentsillustrated in FIG. 23 may be part of the radio modulator 2206 and/orbaseband processor 2208 of FIG. 22. The receiver 2302, may receive anover-the-air signal via the antenna 2304 and demodulates it by passingthrough a mixer 2306, a low-noise amplifier (LNA) 2310, a receive analogfilter 2312, a variable gain amplifier (VGA) 2314, an analog-to-digitalconverter 2316, and a receive digital filter 2318 to obtain OFDMsymbols. A synchronization and automatic gain control (AGC) module 2320may synchronize a frequency synthesizer 2308, the VGA 2314 and aserial-to-parallel converter 2322. The OFDM symbols (from thedemodulated signal) then pass through the serial-to-parallel converter2322, a Fast Fourier Transform (FFT) module 2324, and aparallel-to-serial converter 2326 to obtain coded symbols. The serialdata (coded symbols) then passes through a phase tracker 2330, alog-likelihood ratio (LLR) estimator 2332 that is coupled to a channelestimator 2328, a time and/or frequency de-spreader 2334, and apilot/null/guard tones remover 2336, and a deinterleaver and viterbidecoder 2338 to produce output data 2340. Note that the receiver 2302may include additional components that are not shown in order simplifythe illustration.

According to various features, the receiver may be adapted to receivetransmitted data from a transmitter. In one example, the transmitter mayhave a first mode of operation in which it modulates and transmits dataaccording the ECMA 368 standard. In a second mode of operation, thetransmitter may implement time gating and/or time repetition (aspreviously described) to conserve power during transmissions. Likewise,the receiver 2302 may take advantage of this second mode of operation toalso conserve power.

FIG. 24 is a block diagram illustrating how a receiver may operate whentime gating is used by a transmitter. In one example, one or more of thecomponents illustrated in FIG. 24 may be part of the radio modulator2206 and/or baseband processor 2208 of FIG. 22 or the receiver of FIG.22. The receiver 2402, may receive an over-the-air signal via theantenna 2404 and passes through a band pass filter 2406 and a low-noiseamplifier 2408. The signal is then passed through a mixer 2410, areceive analog filter (e.g., low pass filter) 2412, a variable gainamplifier (VGA) 2414, and an analog-to-digital converter 2416. Thedigitized symbol (in received signal) then passes through a resampler2418 and rotator 2420. A synchronization and automatic gain control(AGC) module 2424 may synchronize a frequency synthesizer 2426 and aphasor generator 2422 coupled to the rotator 2420. The serial digitaldata then passes through an overlap and add module 2428, aserial-to-parallel converter 2430, a Fast Fourier Transform (FFT) module2432, and a parallel-to-serial converter 2434. The serial data thenpasses through a null/guard tone remover 2436 and channel weightingmodule 2440 that is adjusted according to a channel estimator 2438 andphase tracker 2442. A data/pilot extractor 2444 then extracts data orpilots from the signal which then passes through a deinterleaver 2446and viterbi decoder 2448 to produce output data 2450. Note that thereceiver 2402 may include additional components that are not shown inorder simplify the illustration.

The receiver 2402 may be adapted to receive a symbol over a singletransmission at a higher power than typical (as illustrated in FIGS. 13and 14) rather than receiving the same multiple versions of the samesymbol on different frequencies (as illustrated in FIG. 8). Because asymbol is being received just once, various components of the receiver2402 may be cycled Off or slowed down to conserve power. For instance,the FFT module 2432, the VGA 2414, ADC 2416, etc., may be operated at alower speed or cycled Off.

According to one feature, the FFT module 2432 may be slowed down whentime gating is implemented. For example, for data rates 53.3 and 80 Mbps(in the ECMA 368 standard for UWB), the FFT module 2432 may be operatedat one fourth its original speed (since just one symbol is being sentinstead of four). For data rates of 106.7, 160, and 200 Mbps, the FFTmodule 2432 may be operated at one half its original speed (since justone symbol is being sent instead of two).

According to another feature, the FFT module 2432 may instead by cycledOff and On to conserve power during time gating. For example, for datarates 53.3 and 80 Mbps (in the ECMA 368 standard for UWB), the FFTmodule 2432 may be operated just one fourth of the time and cycled Offthree quarters of the time (since just one symbol is being sent insteadof four). For data rates of 106.7, 160, and 200 Mbps, the FFT module2432 may be operated at one half of the time and cycled Off the otherhalf the time (since just one symbol is being sent instead of two).

According to one example of time gating at the receiver, the antenna2404, band pass filter 2406, LNA 2408, mixer 2410, low pass filter 2412,VGA 2414, ADC 2416, and synthesizer 2426 may be cycled Off/On (reducedduty cycle). The resampler 2418, rotator 2420, phasor generator 2422,synchronization estimator 2424, overlap and add module 2428,serial-to-parallel converter 2430, FFT module 2432, parallel-to-serialconverter 2434, null/guard tone remover 2436, channel estimator 2438,channel weighting module 2440, phase tracker 2442, and/or data/pilotextractor 2444 may be cycled Off/On or operated at a lower speed toconserve power.

FIG. 25 is a block diagram illustrating how a receiver may operate whentime repetition is used by a transmitter. In one example, one or more ofthe components illustrated in FIG. 25 may be part of the radio modulator2206 and/or baseband processor 2208 of FIG. 22 or the receiver of FIG.23. The receiver 2502, may receive an over-the-air signal via theantenna 2504 and passes through a band pass filter 2506 and a low-noiseamplifier 2508. The signal is then passed through a mixer 2510, areceive analog filter (e.g., low pass filter) 2512, a variable gainamplifier (VGA) 2514, and an analog-to-digital converter 2516. Thedigitized symbol (in received signal) then passes through a resampler2518 and rotator 2520. A synchronization and automatic gain control(AGC) module 2524 may synchronize a frequency synthesizer 2526 and aphasor generator 2522 coupled to the rotator 2520. The serial digitaldata then passes through an overlap and add module 2528, and aserial-to-parallel converter 2530.

When time repetition is implemented, the receiver 2502 receives eachcopy of the same symbol and processes them individually by the receiverchain. However, the output of the analog components (e.g., the outputfrom the serial-to-parallel converter 2530) is stored (in a buffer 2532)for the first copy symbol and the other copies of the symbol are addedto this stored copy. An FFT module 2534 waits to process the currentsymbol until all copies of the symbol are accumulated in the buffer2532. Therefore, for data rates of 53.3 and 80 Mbps (of the ECMA 368Standard) the FFT module 2534 can be run one fourth of the time (since asymbol is sent four times). Similarly, for data rates data rates 106.7,160 and 200 Mbps the FFT module 2534 can be run one half of the time(since a symbol is sent twice). Another solution is to operate the FFTmodule 2534 to run at one fourth of its normal speed for data rates 53.3and 80 Mbps and one half its typical speed for data rates 106.7, 160 and200 Mbps.

Once processed by the FFT module 2534, the symbol may be furtherprocessed by a parallel-to-serial converter 2538 to produce serial data(obtain coded symbols). The serial data then passes through a null/guardtone remover 2540 and channel weighting module 2542 that is adjustedaccording to a channel estimator 2536 and phase tracker 2546. Adata/pilot extractor 2544 then extracts data or pilots from the signalwhich then passes through a de-interleaver 2548 and Viterbi decoder 2550to produce output data 2552. Note that the receiver 2502 may includeadditional components that are not shown in order simplify theillustration.

The receiver 2502 may be adapted to perform time repetition (asillustrated in FIG. 15). The receiver may receive a symbol on a firsttransmission frequency a plurality of times on different symboltransmission periods, thereby allowing for the accumulation of thevarious retransmissions of the same symbol. Such retransmission of thesame symbol on the same frequency is illustrated in FIG. 15. Because thesymbol is being accumulated, the FFT module 2534 (and possibly othercomponents) in the receiver chain may be cycled Off for longer periodsof time or can run at lower speeds to conserve energy.

According to one example of time repetition, the FFT module 2534,channel estimator 2536, parallel-to-serial converter 2538, null/guardtone remover 2540, channel weighting module 2542, phase tracker 2544,and/or data/pilot extractor 2546 may be cycled Off/On or operated at alower speed to conserve power.

FIG. 26 is a block diagram illustrating a low-power receiver that may beadapted to perform power-conservation. The receiver 2602 may include anantenna 208, a transmission mode detector 2606, and a receiver chain2604. The transmission mode detector may be adapted to receive anindicator from a transmitter device indicating at least one of two modesof symbol transmission. The receiver chain 2604 may receive input data2608 via the antenna 2608 and processes the input data via a RF devices2612, a DAC 2614, a frequency de-spreader 2616, an FFT module 2618, atime de-spreader 2620, a buffer 2622, and a decoder/de-interleaver 2624to produce output data 2626. The receiver chain may be adapted to: (a)receive a symbol according to a first mode where the transmitter deviceenables at least one of time spreading and frequency spreading for aparticular transmission rate, (b) receive the symbol according to asecond mode where the transmitter device disables at least one of timespreading and frequency spreading relative to the first mode of symboltransmission and the same particular data transmission rate; and/or (c)reduce one of either the duty cycle or processing speed of the FastFourier Transform module in the second mode relative to the first modefor the same particular transmission rate. For a first data transmissionrate, the first mode of symbol transmission may utilize time spreadingbut the second mode of symbol transmission disables time spreading. Fora second data transmission rate, the first mode of symbol transmissionutilizes both time spreading and frequency spreading but the second modeof symbol transmission disables at least one of time spreading andfrequency spreading.

FIG. 27 is a block diagram illustrating how power conservation may beachieved using time repetition on a receiver device having multiplemodes of operation. The receiver chain may include radio frequency (RF)devices 2702, a digital-to-analog converter 2704, a frequencyde-spreader 2706, a Fast Fourier Transform (FFT) module 2708, a timede-spreader 2710, and/or a decoder/de-interleaver 2712. A mode selector2716 may control the operation of one or more of the receiver chaincomponents by turning them On or Off, adjusting their duty cycle, and/orslowing their processing speed. Table 2720 illustrates an example of howthe receiver chain components may be operated in a first mode oftransmission (regular operation), in a second mode of transmission(power conservation by time gating), and in a third mode of transmission(power conservation by time repetition). The mode selector 2716 mayconfigure the various receiver chain components as illustrated in table2720. For instance, during power conservation by time gating, the RFDevices 2702 and DAC 2704 may be gated/cycled (e.g., change in dutycycle), the FDS 2706 and/or TDS 2710 may be turned Off, and the FFTmodule 2708 may be cycled Off/On (e.g., reduce its duty cycle) oroperated at a slower speed to achieve power conservation. In anotherinstance, during power conservation by time repetition, the RF Devices2702 and DAC 2704 may be operated normally (without gating/cycling), theFDS 2706 and/or TDS 2710 may be turned Off, and the FFT module 2708 maybe cycled Off/On (e.g., reduce its duty cycle) or operated at a slowerspeed to achieve power conservation.

In various implementations, the mode selector 2716 may cause thereceiver chain to operate according to a regular mode of operation, atime gating power conservation mode, and/or a time repetition powerconservation mode. Note that some implementations of the receiver mayinclude either time gating or time repetition but not both, while otherimplementations may include both time gating and time repetition, thoughnot at the same time.

FIG. 28 illustrates a method for reducing power consumption in wirelessreceiver device. An indicator may be received from a transmitter deviceindicating at least one of two modes of symbol transmission 2802. Adetermination is made as to which mode of symbol transmission isindicated 2804.

In a first mode of symbol transmission, the receiver device enables atleast one of time spreading and frequency spreading for a particulartransmission rate 2806. A Fast Fourier Transform module is operatedaccording a first duty cycle and processing speed 2808. Subsequently, asymbol may be received that is transmitted according to the first mode2810. Time spreading may include the transmission of the same symbol ata plurality of different times over different frequencies. Frequencyspreading may include the concurrent transmission of the same symbolover different frequencies.

In a second mode of symbol transmission, the receiver device disables atleast one of time spreading and frequency spreading relative to thefirst mode of symbol transmission and the same particular transmissionrate 2812. In the second mode, one of either the duty cycle orprocessing speed of the Fast Fourier Transform module is reducedrelative to the first mode for the same particular transmission rate2814. Subsequently, a symbol may be received that is transmittedaccording to the second mode 2816. For a first data transmission rate,the first mode of symbol transmission may utilize time spreading but thesecond mode of symbol transmission disables time spreading. For a seconddata transmission rate, the first mode of symbol transmission mayutilize both time spreading and frequency spreading but the second modeof symbol transmission disables at least one of time spreading andfrequency spreading. The receiver device may be compliant with the ultrawideband European Computer Manufacturers Association (ECMA) 368standard.

In one implementation, when operating according to the second mode, thereceiver may be adapted to receive symbols according to a timerepetition scheme. The same version of a symbol may be received over thesame frequency over a plurality of symbol transmission periods. Thereceived versions of the symbol are then accumulated. The Fast FourierTransform module may be disabled until all versions of the symbol havebeen received to conserve power. The accumulated symbol may then beprocessed using the Fast Fourier Transform module.

In one implementation, when operating according to the second mode, thereceiver may be adapted to receive symbols according to a time gatingscheme. A symbol may be received just once instead of a plurality oftimes over a plurality of symbol transmission periods as in the firstmode, wherein the symbol is transmitted at a higher power than used inthe first mode for the same symbol transmission. The Fast FourierTransform module may be disabled during time periods when the symbolwould have otherwise been retransmitted in the first mode of symboltransmission.

Note that, whether time gating or time repetition is used during a powerconservation mode, the effective data transmission rate may remain thesame during the power conservation mode relative to a normal mode ofoperation.

It should be recognized that, generally, most of the processingdescribed in this disclosure may be implemented in a similar fashion.Any of the circuit(s) or circuit sections may be implemented alone or incombination as part of an integrated circuit with one or moreprocessors. The one or more of the circuits may be implemented on anintegrated circuit, an Advance RISC Machine (ARM) processor, a digitalsignal processor (DSP), a general purpose processor, etc.

Also, it is noted that the embodiments may be described as a processthat is depicted as a flowchart, a flow diagram, a structure diagram, ora block diagram. Although a flowchart may describe the operations as asequential process, many of the operations can be performed in parallelor concurrently. In addition, the order of the operations may bere-arranged. A process is terminated when its operations are completed.A process may correspond to a method, a function, a procedure, asubroutine, a subprogram, etc. When a process corresponds to a function,its termination corresponds to a return of the function to the callingfunction or the main function.

As used in this application, the terms “component,” “module,” “system,”and the like are intended to refer to a computer-related entity, eitherhardware, firmware, a combination of hardware and software, software, orsoftware in execution. For example, a component may be, but is notlimited to being, a process running on a processor, a processor, anobject, an executable, a thread of execution, a program, and/or acomputer. By way of illustration, both an application running on acomputing device and the computing device can be a component. One ormore components can reside within a process and/or thread of executionand a component may be localized on one computer and/or distributedbetween two or more computers. In addition, these components can executefrom various computer readable media having various data structuresstored thereon. The components may communicate by way of local and/orremote processes such as in accordance with a signal having one or moredata packets (e.g., data from one component interacting with anothercomponent in a local system, distributed system, and/or across a networksuch as the Internet with other systems by way of the signal).

Moreover, a storage medium may represent one or more devices for storingdata, including read-only memory (ROM), random access memory (RAM),magnetic disk storage mediums, optical storage mediums, flash memorydevices and/or other machine readable mediums for storing information.The term “machine readable medium” includes, but is not limited toportable or fixed storage devices, optical storage devices, wirelesschannels and various other mediums capable of storing, containing orcarrying instruction(s) and/or data.

Furthermore, embodiments may be implemented by hardware, software,firmware, middleware, microcode, or any combination thereof. Whenimplemented in software, firmware, middleware or microcode, the programcode or code segments to perform the necessary tasks may be stored in amachine-readable medium such as a storage medium or other storage(s). Aprocessor may perform the necessary tasks. A code segment may representa procedure, a function, a subprogram, a program, a routine, asubroutine, a module, a software package, a class, or any combination ofinstructions, data structures, or program statements. A code segment maybe coupled to another code segment or a hardware circuit by passingand/or receiving information, data, arguments, parameters, or memorycontents. Information, arguments, parameters, data, etc. may be passed,forwarded, or transmitted via any suitable means including memorysharing, message passing, token passing, network transmission, etc.

One or more of the components, steps, and/or functions illustrated inthe FIGs. may be rearranged and/or combined into a single component,step, or function or embodied in several components, steps, or functionswithout affecting the operation of the pseudo-random number generation.Additional elements, components, steps, and/or functions may also beadded without departing from the invention. The apparatus, devices,and/or components illustrated in the Figures may be configured toperform one or more of the methods, features, or steps described in theFigures. The novel algorithms described herein may be efficientlyimplemented in software and/or embedded hardware.

Those of skill in the art would further appreciate that the variousillustrative logical blocks, modules, circuits, and algorithm stepsdescribed in connection with the embodiments disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system.

The various features of the invention described herein can beimplemented in different systems without departing from the invention.For example, some implementations of the invention may be performed witha moving or static communication device (e.g., access terminal) and aplurality of mobile or static base stations (e.g., access points).

It should be noted that the foregoing embodiments are merely examplesand are not to be construed as limiting the invention. The descriptionof the embodiments is intended to be illustrative, and not to limit thescope of the claims. As such, the present teachings can be readilyapplied to other types of apparatuses and many alternatives,modifications, and variations will be apparent to those skilled in theart.

We claim:
 1. A method to reduce power consumption in a wirelesscommunication device, the method comprising: utilizing a first symboltransmission mode in which diversity is enabled at a particulartransmission rate if a wireless channel characteristic is above athreshold level, the wireless channel characteristic characterizing awireless channel; and utilizing a second symbol transmission mode inwhich diversity is disabled at a particular transmission rate if thewireless channel characteristic is below the threshold level.
 2. Themethod of claim 1, wherein utilizing a first symbol transmission mode inwhich diversity is enabled comprises enabling at least one of timespreading and frequency spreading.
 3. The method of claim 1, whereinutilizing a second symbol transmission mode in which diversity isdisabled comprises disabling at least one of time spreading andfrequency spreading.
 4. The method of claim 1, further comprisingdetermining the wireless channel characteristic based on at least one ofa desired signal strength, channel noise, a noise floor, or aninterference level.
 5. The method of claim 1, wherein for a first datatransmission rate the first mode of symbol transmission utilizes timespreading but the second mode of symbol transmission disables timespreading.
 6. The method of claim 1, wherein for a second datatransmission rate the first mode of symbol transmission utilizes bothtime spreading and frequency spreading and the second mode of symboltransmission disables at least one of time spreading and frequencyspreading.
 7. The method of claim 1, further comprising: transmitting asymbol using at least one of time spreading and frequency spreading ifthe first mode of symbol transmission is selected; and transmitting asymbol while disabling at least one of time spreading and frequencyspreading which is enabled in the first mode of symbol transmission ifthe second mode of symbol transmission is selected.
 8. The method ofclaim 1, wherein the transmitter is compliant with the ultra widebandEuropean Computer Manufacturers Association (ECMA) 368 standard.
 9. Themethod of claim 1, further comprising sending an indicator to a receiverdevice indicating a status associated with the enablement ordis-enablement of diversity.
 10. The method of claim 1, whereinutilizing a second symbol transmission mode in which diversity isdisabled comprises: enabling at least one of time grating and timerepetition.
 11. The method of claim 10, wherein time grating comprises:transmitting a symbol to a receiver using a single time frame.
 12. Themethod of claim 10, wherein time repetition comprises: transmitting asymbol to a receiver using a plurality of time frames at a singlefrequency.
 13. The method of claim 1, further comprising: determining apower level to transmit a symbol to a receiver using a single timeframe, the determined power level being proportional to the plurality oftime frames used to transmit the symbol when diversity utilized by thefirst symbol transmission mode is enabled.
 14. The method of claim 1,further comprising: determining a difference between a plurality of timeframes used to transmit a symbol when diversity utilized by the firstsymbol transmission mode is enabled and a single time frame.
 15. Themethod of claim 14, further comprising: reducing a time period ofoperational status of an inverse Fast Fourier Transform module based onthe determined difference.
 16. The method of claim 1, furthercomprising: transmitting an indicator to a receiver, wherein theindicator indicates whether time grating or time repetition has beenenabled with the second symbol transmission mode.
 17. A wirelesscommunication device, the device comprising: a transmitter chaincomprising at least one of a time spreader and frequency spreader,wherein the transmitter chain is adapted to: select a first mode ofsymbol transmission in which diversity is enabled at a particulartransmission rate if the wireless channel characteristic is above athreshold level; and select a second mode of symbol transmission inwhich diversity is disabled at the same particular transmission rate ifthe wireless channel characteristic is below the threshold level. 18.The wireless communication device of claim 17, wherein enablingdiversity comprises enabling at least one of time spreading andfrequency spreading.
 19. The wireless communication device of claim 17,wherein disabling diversity comprises disabling at least one of timespreading and frequency spreading.
 20. The wireless transmitter deviceof claim 17, wherein the transmitter chain is further adapted to: sendan indicator to the receiver device that at least one of time spreaderand frequency spreader are disabled.
 21. The wireless transmitter deviceof claim 20, wherein during the second mode of symbol transmission thetransmitter chain is adapted to: modulate a symbol into a firstfrequency using an inverse Fast Fourier Transform module; store themodulated symbol; transmit the modulated symbol to the receiver deviceon a symbol transmission period; retransmit the stored modulated symbolto the receiver device during other symbol transmission periods; anddisable the inverse Fast Fourier Transform module during the othersymbol transmission periods when retransmitting the stored modulatedsymbol to conserve power.
 22. The wireless transmitter device of claim20, wherein during the second mode of symbol transmission thetransmitter chain is adapted to: generate a symbol for transmissionusing an inverse Fast Fourier Transform module; transmit the symbol justonce to a receiver device using greater transmission power than used inthe first mode of symbol transmission to transmit symbols; and disablethe inverse Fast Fourier Transform module during time periods when thesymbol would have otherwise been retransmitted in the first mode ofsymbol transmission.
 23. The wireless communication device of claim 17,wherein disabling diversity in the second mode of symbol transmissionmode in causes the transmitter chain to be further adapted to: enable atleast one of time grating and time repetition.
 24. The wirelesscommunication device of claim 23, wherein enabling time grating causesthe transmitter chain to be further adapted to: transmit a symbol to areceiver using a single time frame.
 25. The wireless communicationdevice of claim 23, wherein enabling time repetition causes thetransmitter chain to be further adapted to: transmit a symbol to areceiver using a plurality of time frames at a single frequency.
 26. Thewireless communication device of claim 17, wherein the transmitter chainis further adapted to: determine a power level to transmit a symbol to areceiver using a single time frame, the determined power level beingproportional to the plurality of time frames used to transmit the symbolwhen diversity utilized by the first mode of symbol transmission isenabled.
 27. The wireless communication device of claim 17, wherein thetransmitter chain is further adapted to: determine a difference betweena plurality of time frames used to transmit a symbol when diversityutilized by the first mode of symbol transmission mode is enabled and asingle time frame.
 28. The wireless communication device of claim 27,wherein the transmitter chain is further adapted to: reduce a timeperiod of operational status of an inverse Fast Fourier Transform modulebased on the determined difference.
 29. The wireless communicationdevice of claim 17, wherein the transmitter chain is further adapter to:transmit an indicator to a receiver, the indicator indicating whethertime grating or time repetition has been enabled with the second mode ofsymbol transmission.